This invention concerns a process for preparing alkylanthraquinone. Known processes for preparing alkylanthraquinones include the following:
I. HEATING ALKYLBENZOYLBENZOIC ACID IN A STOICHIOMETRIC EXCESS OF SULFURIC ACID OR OLEUM AT BELOW 100.degree.C,
ii. heating methyl- or ethyl -benzoylbenzoic acid in the presence of catalytic amounts of oleum at temperatures of 100.degree. C to 300.degree. C in the presence of up to 25% of an inert solvent, e.g. trichlorobenzene, based on the weight of the benzoylbenzoic acid.
Said processes suffer from several infirmities: type (i) processes are slow and tend toward low yields of alkylanthraquinones whose alky groups contain more than two carbon atoms; type (ii) processes present handling difficulties because of the high temperatures employed, said high temperatures also tending to cause decomposition of the alkylanthraquinones whose alkyl groups contain more than one or two carbon atoms.
Patents which are representative of the state of this art include: U.S. Pat. No. 2,842,562 (catalytic amount of sulfuric acid or oleum); U.S. 3,032,560 (no solvent is present during the reaction); U.S. Pat. No. 1,856,231 (produces a nitroanthraquinone); U.S. 1,890,040 (condensation reaction of a quinone with a 1,3 butadiene hydrocarbon); German Pat. No. 2,058,121 (sulfur trioxide is the cyclization agent); and French 1,528,795 (no solvent is present during the reaction).